It wasn't a difficult application form to fill in. I have no idea how they chose people, but to be honest I don't think there's any reason to provide feedback. I doubt it would be of any real use to the people who applied.
If you look at the costs of the time it would take to produce a mail merge data spreadsheet, the time to produce a letter, stuff envelopes and then actually pay to post them, it would all add up.
Yes it may be nice for people to be told they haven't been successful for a job, but in my experience this just doesn't tend to happen much. Be it a casual job like this or a career type job.
In my opinion I don't think the club have done anything wrong as essentially they have let the unsuccessful applicants know on the official site.